CN114730651A

CN114730651A - Method for producing sulfide solid electrolyte

Info

Publication number: CN114730651A
Application number: CN202080080351.1A
Authority: CN
Inventors: 井关勇介; 中谷展人
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2019-11-21
Filing date: 2020-11-20
Publication date: 2022-07-08
Also published as: JPWO2021100874A1; JP6896202B1; US20220041444A1; DE112020005721T5; WO2021100874A1; US11746014B2

Abstract

The present invention relates to a method for producing a sulfide solid electrolyte, including a step of subjecting a slurry to at least one treatment selected from drying and heating, the method comprising: mixing a solid electrolyte raw material containing lithium element, sulfur element, phosphorus element and halogen element with a complexing agent in a reaction tank to obtain complex slurry containing a complex formed by the solid electrolyte raw material and the complexing agent; transferring the complex slurry to an intermediate tank provided with a cooling device for cooling.

Description

Method for producing sulfide solid electrolyte

Technical Field

The present invention relates to a method for producing a sulfide solid electrolyte.

Background

In recent years, as information-related devices such as personal computers, video cameras, and cellular phones, and communication devices have rapidly spread, the development of batteries used as power sources thereof has been attracting attention. In the past, in batteries used for such applications, an electrolyte solution containing a flammable organic solvent was used, but by making the battery all solid, the safety device was simplified without using a flammable organic solvent in the battery, and the manufacturing cost and productivity were excellent, so that development of all solid batteries in which the electrolyte solution was replaced with a solid electrolyte layer was carried out.

The solid-state electrolyte used as the solid electrolyte layer is broadly classified into a solid-phase method and a liquid-phase method, and in recent years, the liquid-phase method has attracted attention as a method for mass production of a solid electrolyte easily in addition to versatility and applicability for practical use of all-solid-state batteries. The liquid phase method includes a homogeneous method using a solution of a solid electrolyte material and a heterogeneous method using a suspension (slurry) in which a solid-liquid coexists without completely dissolving a solid electrolyte material.

In the liquid phase method, a solution (or slurry) of a complexing agent of a solid electrolyte raw material is generated, the solution is dried to obtain a complex crystal, and then the complex crystal is fired to obtain a solid electrolyte of another crystal (see patent document 1). In particular, in order to obtain a uniform solid electrolyte, there is an advantage via a homogeneous method in which the electrolyte is completely dissolved in a solvent in a solution state (see non-patent document 1). Such a method is not limited to the field of solid electrolytes, and is also studied in a method for manufacturing a solar cell (see patent document 2).

Documents of the prior art

Patent document

Patent document 1: international publication No. 2018/054709 booklet

Patent document 2: japanese laid-open patent publication No. 2015-526884

Non-patent document

Non-patent document 1: J.Jpn.Soc.colour Mater 89 (symbol of color Material Association), 9, 300-305(2016)

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a sulfide solid electrolyte having high ionic conductivity by suppressing a decrease in ionic conductivity in mass production scale production.

Solution for solving the above technical problem

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found that the problems can be solved by a method for producing a sulfide solid electrolyte comprising a step of subjecting a slurry to at least one treatment selected from drying and heating, the method comprising: mixing a solid electrolyte raw material containing lithium element, sulfur element, phosphorus element and halogen element with a complexing agent in a reaction tank to obtain complex slurry containing a complex formed by the solid electrolyte raw material and the complexing agent; transferring the complex slurry to an intermediate tank provided with a cooling device for cooling.

Effects of the invention

According to the present invention, it is possible to provide a production method that suppresses a decrease in ion conductivity due to separation of specific components and thereby obtains a sulfide solid electrolyte having high ion conductivity, even if a heterogeneous method using a slurry is employed in the production process.

Drawings

Fig. 1 is a flowchart illustrating an example of a preferred embodiment of the manufacturing method of the present embodiment.

Fig. 2 is a flowchart illustrating an example of a preferred embodiment of the manufacturing method of the present embodiment.

Fig. 3 is a flowchart illustrating an example of a preferred embodiment of an apparatus used in the manufacturing method of the present embodiment.

Fig. 4 is an X-ray diffraction spectrum of the sulfide solid electrolytes obtained in reference example 1, and comparative example 1.

FIG. 5 shows solid electrolyte raw materials used in examples, amorphous and crystalline Li of reference examples 1 and 2₃PS₄X-ray diffraction spectrum of (a).

Fig. 6 is an X-ray diffraction spectrum of the complex, amorphous sulfide solid electrolyte, and crystalline sulfide solid electrolyte obtained in reference example 1.

Detailed Description

Hereinafter, embodiments of the present invention (hereinafter, may be referred to as "the present embodiment") will be described. In the present specification, the numerical values of the upper limit and the lower limit in the numerical ranges of "above", "below" and "to" are numerical values that can be arbitrarily combined, and the numerical values of the examples can also be used as the numerical values of the upper limit and the lower limit.

(findings obtained by the inventors to complete the present invention)

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found the following, and have completed the present invention.

In the liquid phase method, since uniform dispersion is achieved by dissolution of the raw material, manufacturing conditions capable of dissolution are studied, but in the synthesis of a sulfide solid electrolyte using a multicomponent raw material, it is difficult to uniformly dissolve and synthesize each component of a complexing agent solution or slurry without separation. The present applicant has made studies on the use of various complexing agents and the like in a heterogeneous method in which solid and liquid coexist, and as a general tendency, it has been found that the ion conductivity of a solid electrolyte tends to decrease when the mass production scale is reached.

The present inventors have intensively studied about the tendency of the decrease in the ion conductivity, and as a result, have found that, particularly in the heterogeneous method in which solid-liquid coexists, a specific component derived from a halogen element such as lithium bromide or lithium iodide, or a lithium element (hereinafter, sometimes simply referred to as "specific component") which is preferably used as a raw material of a solid electrolyte is easily separated. If the specific component is separated, a desired compound structure cannot be obtained, and thus the ion conductivity of the solid electrolyte may be lowered. Furthermore, on a mass production scale, it is difficult to maintain the dispersion state of each component or suppress the separation of specific components through a series of production steps such as a mixing step of a slurry containing a solid electrolyte raw material or the like, and it is difficult to obtain a sulfide solid electrolyte having a desired crystal structure or the like and high ion conductivity.

As described above, in the production of a sulfide solid electrolyte, it is important to maintain the specific component without separating it from the complex in order to obtain high ion conductivity, and therefore, a complexing agent is used in the production method of the present embodiment. On the other hand, it has also been found that even if a complexing agent is used, if the complex is maintained in a slurry state, a specific component is separated from the complex with time, resulting in a decrease in ion conductivity. The situation in which the complex is held in the state of a slurry may occur in the production of a laboratory-grade solid electrolyte, but in the future, if the complex is produced on a mass production scale, it is expected that the situation in which the complex is held in the state of a slurry will be long due to production adjustment, equipment failure, or the like, and the ionic conductivity will be lowered. In the production method of the present embodiment, the complex slurry is cooled and stored, whereby the separation of the specific component from the complex can be suppressed as much as possible, and high ionic conductivity can be obtained.

Thus, the production method of the present embodiment can cope not only with a case where a sulfide solid electrolyte having a higher ion conductivity is obtained, but also with a case where drying, heating, or the like, which will be described later, cannot be performed for a short time, for example, within 12 hours, within 6 hours, within 1 hour, or the like, after the complex slurry is prepared in the production process of the sulfide solid electrolyte, that is, with a case where the complex is held in the state of the complex slurry for a long time, and can be said to be an effective production method.

Further, the reason why the separation can be suppressed by retaining the specific component in the complex in the cold storage is considered to be that the PS is linked to the complex via the hetero element in the complexing agent₄The binding force between the lithium element of the structure such as the structure and the lithium element such as the lithium halide is maintained, and the chemical stability of the aggregate formed via the complexing agent in the complex slurryThe mechanism of the mechanism is not clear. If the polymer is completely dissolved or completely undissolved in a predetermined temperature range, the influence of solubility is not exerted (for example, patent document 2).

However, since the complex slurry of the present embodiment coexists in a solid-liquid state, each component of the complex having different solubilities is dissolved or not dissolved and contained in the slurry. Since the solubility varies depending on the temperature, it is generally considered to be desirable to maintain the dissolved state of the complex slurry by keeping the temperature of the complex slurry constant. In addition, no change was observed in visual observation when the complex slurry was held for a long period of time, regardless of the presence or absence of cold storage. Therefore, it is difficult to find a problem related to chemical stability of the complex slurry.

However, surprisingly, in the production method of the present embodiment, it has been found that by performing only a simple operation of cooling and storing a complex slurry containing a complex formed from a predetermined element and a complexing agent, excellent effects are obtained that the chemical stability of the aggregate formed via the complexing agent in the complex slurry can be obtained, separation of bromine element and lithium element derived from a specific component, particularly lithium bromide that is easily separated, can be suppressed, and a sulfide solid electrolyte having a higher ionic conductivity can be obtained.

[ method for producing sulfide solid electrolyte ]

A method for producing a sulfide solid electrolyte according to the present embodiment is a method for producing a sulfide solid electrolyte including a step of subjecting a slurry to at least one treatment selected from drying and heating, the method including: mixing a solid electrolyte raw material containing lithium element, sulfur element, phosphorus element and halogen element with a complexing agent in a reaction tank to obtain complex slurry containing a complex formed by the solid electrolyte raw material and the complexing agent; transferring the complex slurry to an intermediate tank provided with a cooling device for cooling.

The "method for producing a sulfide solid electrolyte including a step of subjecting a slurry to at least one treatment selected from drying and heating" means that, in the production method of the present embodiment, a heterogeneous method among liquid-phase methods is employed, that is, a slurry in which solid and liquid coexist is used by using a solvent that does not completely dissolve a solid electrolyte raw material. In the present embodiment, as the slurry, there may be mainly a slurry containing a solid electrolyte raw material, a complex slurry containing a complex described later, or the like, or there may be a slurry containing at least one selected from the solid electrolyte raw material, the complex, and a sulfide solid electrolyte obtained by reacting a part of the raw material. In any case, the production method of the present embodiment is not necessarily limited to the liquid phase method, and may be any method.

In the present specification, "sulfide solid electrolyte" refers to an electrolyte that contains at least sulfur element and maintains a solid at 25 ℃ under a nitrogen atmosphere. The sulfide solid electrolyte obtained by the production method of the present embodiment is a solid electrolyte containing lithium element, sulfur element, phosphorus element, and halogen element, and having ion conductivity due to lithium element.

The "sulfide solid electrolyte" includes both a crystalline sulfide solid electrolyte having a crystal structure and an amorphous sulfide solid electrolyte. In the present specification, the crystalline sulfide solid electrolyte refers to a solid electrolyte in which peaks derived from the sulfide solid electrolyte are observed in an X-ray diffraction pattern in X-ray diffraction measurement, and is a material that is independent of peaks of raw materials having no active self-solid electrolyte among the peaks. That is, the crystalline sulfide solid electrolyte includes a crystal structure derived from the sulfide solid electrolyte, and may have a crystal structure in which a part thereof is derived from the sulfide solid electrolyte, or may have a crystal structure in which the whole thereof is derived from the sulfide solid electrolyte. Further, as long as the crystalline sulfide solid electrolyte has the above-described X-ray diffraction pattern, an amorphous sulfide solid electrolyte may be included in a part thereof. Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating the amorphous sulfide solid electrolyte to a crystallization temperature or higher.

In the present specification, the term "amorphous sulfide solid electrolyte" means that the X-ray diffraction pattern is a halo pattern (halo pattern) in which a peak derived from a material other than the peak is not substantially observed in the X-ray diffraction measurement, and is independent of the peak of the raw material in which the passive auto-sulfide solid electrolyte is present.

In the method for producing a sulfide solid electrolyte according to the present embodiment, it is preferable that Li is used or not₃PS₄The solid electrolyte includes the following four embodiments as a solid electrolyte material or whether a solvent is used. Examples of preferred embodiments of these four embodiments are shown in fig. 1 (embodiments a and B) and fig. 2 (embodiments C and D). That is, the manufacturing method of the present embodiment preferably includes: embodiment A) a method for producing a lithium secondary battery using a raw material such as lithium sulfide or phosphorus pentasulfide and a complexing agent; (embodiment B) containing Li as the main structure of the electrolyte₃PS₄A method of producing a solid electrolyte using a complexing agent as a raw material; (embodiment C) a method for producing a lithium secondary battery according to embodiment a, wherein a solvent is added to a raw material such as lithium sulfide and a complexing agent; (embodiment D) in the above-mentioned embodiment B, Li as a raw material₃PS₄And adding a solvent into the solid electrolyte and the complexing agent.

Embodiments a to D will be described below in order.

(embodiment A)

As shown in fig. 1, embodiment a is as follows: the method for producing a sulfide solid electrolyte includes a step of subjecting a slurry to at least one treatment selected from drying and heating, and is characterized by including a step of mixing a solid electrolyte raw material containing a lithium element, a sulfur element, a phosphorus element, and a halogen element with a complexing agent in a reaction vessel. The solid electrolyte raw material and the complexing agent are mixed in the reaction tank to obtain a complex slurry containing a complex formed by the solid electrolyte raw material and the complexing agent, and the slurry is cooled to obtain the sulfide solid electrolyte. In embodiment a, it is preferable that the method includes at least one step selected from drying and heating after cooling and storing.

The production method of the present embodiment preferably includes pulverizing the complex, and the complex contained in the complex slurry includes the complex after the pulverization. In addition, in the case where heating is included after pulverization, cooling and storage are preferably performed after pulverization and before heating, that is, the pulverization is preferably performed at the time of mixing (simultaneously with mixing) or after mixing and before cooling and storage.

Hereinafter, the description will be given of embodiment a, but what is described as "this embodiment" is what can be applied to other embodiments.

(solid electrolyte raw material)

The solid electrolyte material used in the present embodiment contains lithium element, sulfur element, phosphorus element, and halogen element, and specifically, at least one or more materials selected from materials containing at least one of these elements are used.

As the raw material (compound) containing at least one of lithium element, sulfur element, phosphorus element, and halogen element, for example, included in the solid electrolyte raw material, lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; phosphorus trisulfide (P)₂S₃) Phosphorus pentasulfide (P)₂S₅) Phosphorus sulfide; various Phosphorus Fluorides (PF)₃、PF₅) Various phosphorus chlorides (PCl)₃、PCl₅、P₂Cl₄) Various phosphorus bromides (PBr)₃、PBr₅) Various Phosphorus Iodides (PI)₃、P₂I₄) And the like phosphorus halides; thiophosphoryl fluoride (PSF)₃) Thiophosphoryl chloride (PSCl)₃) Thiophosphoryl bromide (PSBr)₃) Thiophosphoryl iodide (PSI)₃) Thiophosphoryl fluoride dichloride (PSCl)₂F) Thiophosphoryl fluorodibromo (PSBr)₂F) Halogenated thiophosphoryl groups; a raw material composed of at least two elements selected from the four elements, fluorine (F)₂) Chlorine (Cl)₂) Bromine (Br)₂) Iodine (I)₂) Etc. halogen monomers, preferably bromine (Br)₂) Iodine (I)₂)。

Examples of the material that can be used as the raw material other than the above include a raw material containing at least one element selected from the above four elements and containing elements other than the four elements, and more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS )₂) Metal sulfides such as aluminum sulfide and zinc sulfide; phosphoric acid compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium, such as sodium halides, e.g., sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; halogenated metals such as aluminum halide, silicon halide, germanium halide, arsenic halide, selenium halide, tin halide, antimony halide, tellurium halide, and bismuth halide; phosphorus oxychloride (POCl)₃) Phosphorus oxybromide (POBr)₃) Phosphorus oxide of halogen, etc.; and the like.

As the solid electrolyte raw material, any one suitable for obtaining a desired crystal structure may be appropriately selected from the above, and from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ionic conductivity, among the above, lithium sulfide is preferable; phosphorus trisulfide (P)₂S₃) Phosphorus pentasulfide (P)₂S₅) Phosphorus sulfides; fluorine (F)₂) Chlorine (Cl)₂) Bromine (Br)₂) Iodine (I)₂) And the like halogen monomers; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

Examples of the combination of the raw materials include a combination of a raw material containing a lithium element, a sulfur element, and a phosphorus element such as lithium sulfide and phosphorus pentasulfide, and a raw material containing a halogen element such as lithium halide; a combination of a raw material containing a lithium element, a sulfur element, and a phosphorus element, such as lithium sulfide and phosphorus pentasulfide, and a raw material containing a halogen element, such as a halogen monomer, is preferably lithium bromide and lithium iodide as a lithium halide, chlorine, bromine, and iodine as a halogen monomer, and more preferably bromine and iodine.

The lithium sulfide used in embodiment a is preferably a particle.

Average particle diameter (D) of lithium sulfide particles₅₀) Preferably 10 to 2000 μm, more preferably 30 to 1500 μm, and still more preferably 50 to 1000 μm. In the present specification, the average particle diameter (D)₅₀) The volume distribution is, for example, an average particle diameter that can be measured using a laser diffraction/scattering particle size distribution measuring apparatus. Among the materials exemplified as the above-mentioned raw materials, the solid raw material is preferably a solid raw material having an average particle diameter similar to that of the lithium sulfide particles, that is, a solid raw material having an average particle diameter in the same range as that of the lithium sulfide particles.

In the case where lithium sulfide, phosphorus pentasulfide, and lithium halide are used as raw materials, the proportion of lithium sulfide to the total of lithium sulfide and phosphorus pentasulfide is preferably 70 to 80 mol%, more preferably 72 to 78 mol%, and even more preferably 74 to 76 mol%, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity.

When lithium sulfide, phosphorus pentasulfide, lithium halide and other raw materials used as needed are used, the content of lithium sulfide and phosphorus pentasulfide to the total of these raw materials is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and still more preferably 70 to 80 mol%.

In addition, when lithium bromide and lithium iodide are used in combination as lithium halide, the proportion of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 45 to 65 mol%, from the viewpoint of improving the ionic conductivity.

When a halogen monomer is used as a raw material and lithium sulfide and phosphorus pentasulfide are used, the ratio of the number of moles of lithium sulfide obtained by removing the same number of moles of lithium sulfide as the number of moles of the halogen monomer to the total number of moles of lithium sulfide and phosphorus pentasulfide obtained by removing the same number of moles of lithium sulfide as the number of moles of the halogen monomer is preferably in the range of 60 to 90%, more preferably in the range of 65 to 85%, even more preferably in the range of 68 to 82%, even more preferably in the range of 72 to 78%, and particularly preferably in the range of 73 to 77%. This is because, in these proportions, higher ion conductivity can be obtained. From the same viewpoint, when lithium sulfide, phosphorus pentasulfide and a halogen monomer are used, the content of the halogen monomer relative to the total amount of lithium sulfide, phosphorus pentasulfide and the halogen monomer is preferably 1 to 50 mol%, more preferably 2 to 40 mol%, even more preferably 3 to 25 mol%, and even more preferably 3 to 15 mol%.

When lithium sulfide, phosphorus pentasulfide, a halogen monomer, and lithium halide are used, the content (α mol%) of the halogen monomer with respect to the total amount of these and the content (β mol%) of the lithium halide with respect to the total amount of these preferably satisfy the following formula (2), more preferably satisfy the following formula (3), still more preferably satisfy the following formula (4), and still more preferably satisfy the following formula (5).

2≤2α+β≤100…(2)

4≤2α+β≤80…(3)

6≤2α+β≤50…(4)

6≤2α+β≤30…(5)

When two halogen monomers are used, assuming that the number of moles of one halogen element is a1 and the number of moles of the other halogen element is a2, a 1: a2 is preferably 1-99: 99-1, more preferably 10: 90-90: 10, more preferably 20: 80-80: 20, more preferably 30: 70-70: 30.

when the two halogen monomers are bromine and iodine, if the number of moles of bromine is B1 and the number of moles of iodine is B2, B1: b2 is preferably 1-99: 99-1, more preferably 15: 85-90: 10, more preferably 20: 80-80: 20, more preferably 30: 70-75: 25, particularly preferably 35: 65-75: 25.

(complexing agent)

The method for producing a sulfide solid electrolyte according to the present embodiment uses a complexing agent. In the present specification, the complexing agent is a substance capable of forming a complex with lithium element, and has a property of promoting the formation of the complex by reacting with a sulfide, a halide, or the like containing lithium element contained in the solid electrolyte raw material. Thus, if a complexing agent is not used, it is difficult to form a complex, separation of a specific component cannot be suppressed, and high ionic conductivity cannot be obtained.

The complexing agent is not particularly limited as long as it has the above properties, and a compound containing an element having a high affinity for lithium element, for example, a hetero element such as nitrogen element, oxygen element, or chlorine element is particularly preferable, and a compound having a group containing such a hetero element is more preferable. This is because these hetero elements and the group containing the hetero element can coordinate (bond) with lithium.

The complexing agent is considered to be a substance having the following properties: the hetero element in the molecule has high affinity for lithium atoms, and is likely to be involved in PS, which is a representative structure existing as a main structure in the sulfide solid electrolyte obtained by the production method of the present embodiment₄Li of structure₃PS₄Or a lithium-containing structure, or a lithium-containing raw material such as a lithium halide is bonded to form an aggregate. In the present embodiment, the "complex formed by the solid electrolyte raw material and the complexing agent" is a general term for these structures and aggregates, and is preferably formed by the complexing agent, lithium element, sulfur element, phosphorus element, and halogen element. Therefore, it is considered that PS is produced by mixing the solid electrolyte raw material with a complexing agent₄A lithium-containing structure such as a structure or an aggregate via a complexing agent, a lithium-containing raw material such as lithium halide or an aggregate via a complexing agent are present all over, and a complex in which a halogen element is fixed in a more dispersed state is obtained.

Therefore, it is preferable to have at least two hetero elements capable of coordinating (bonding) in the molecule, and it is more preferable to have a group containing at least two hetero elements in the molecule. By having in the molecule at least two hetero atomsA group of elements, thereby enabling to contain PS₄Li of structure₃PS₄And the lithium-containing structure and the lithium-containing raw material such as lithium halide are bonded via at least two hetero elements in the molecule, so that the halogen element is fixed in a more dispersed manner in the complex, and the decrease in the ion conductivity due to the separation of these specific components can be suppressed, and as a result, a sulfide solid electrolyte having high ion conductivity can be obtained. Further, among the hetero elements, a nitrogen element is preferable, and as the group containing a nitrogen element, an amino group is preferable, that is, an amine compound is preferable as a complexing agent.

The amine compound is not particularly limited as long as it has an amino group in the molecule to promote the formation of a complex, and a compound having at least two amino groups in the molecule is preferable. By having such a structure, it is possible to include PS₄Li of structure₃PS₄And the lithium-containing structure and a lithium-containing raw material such as a lithium halide are bonded via at least two nitrogen elements in the molecule, and therefore the halogen element is fixed in a more dispersed manner in the complex, and as a result, a sulfide solid electrolyte having high ionic conductivity can be obtained.

Examples of such amine compounds include amine compounds such as aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these amine compounds can be used alone or in combination of two or more.

More specifically, the aliphatic amine is typically preferably an aliphatic primary diamine such as ethylenediamine, diaminopropane or diaminobutane; aliphatic secondary diamines such as N, N '-dimethylethylenediamine, N' -diethylethylenediamine, N '-dimethyldiaminopropane, and N, N' -diethyldiaminopropane; aliphatic tertiary diamines such as N, N '-tetramethyldiaminomethane, N' -tetramethylethylenediamine, N '-tetraethylethylenediamine, N' -tetramethyldiaminopropane, N '-tetraethyldiaminopropane, N' -tetramethyldiaminobutane, N '-tetramethyldiaminopentane, and N, N' -tetramethyldiaminohexane; and aliphatic diamines. In the examples given in the present specification, if the compound is diaminobutane, unless otherwise specified, the compound includes all isomers such as linear and branched isomers in addition to isomers related to the position of an amino group such as 1, 2-diaminobutane, 1, 3-diaminobutane and 1, 4-diaminobutane.

The aliphatic amine preferably has 2 or more, more preferably 4 or more, and still more preferably 6 or more carbon atoms, and the upper limit is preferably 10 or less, more preferably 8 or less, and still more preferably 7 or less carbon atoms. The number of carbon atoms of the hydrocarbon group of the aliphatic hydrocarbon group in the aliphatic amine is preferably 2 or more, and the upper limit is preferably 6 or less, more preferably 4 or less, and further preferably 3 or less.

As the alicyclic amine, alicyclic primary diamines such as cyclopropanediamine and cyclohexanediamine; alicyclic secondary diamines such as bisaminomethylcyclohexane; alicyclic tertiary diamines such as N, N' -tetramethyl-cyclohexanediamine and bis (ethylmethylamino) cyclohexane; alicyclic diamines and the like, and heterocyclic amines include, as a representative example, heterocyclic primary diamines such as isophorone diamine; heterocyclic secondary diamines such as piperazine and dipiperidinopropane; heterocyclic tertiary diamines such as N, N-dimethylpiperazine and dimethylpiperidine; and the like heterocyclic diamines.

The alicyclic amine or heterocyclic amine preferably has 3 or more, more preferably 4 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less.

Further, as the aromatic amine, typically, aromatic primary diamines such as phenylenediamine, toluenediamine, and naphthalenediamine; aromatic secondary diamines such as N-methylphenylenediamine, N '-dimethylphenylenediamine, N' -dimethylnaphthylenediamine and N-naphthylethylenediamine; aromatic tertiary diamines such as N, N-dimethylphenylenediamine, N ' -tetramethylphenylenediamine, N ' -tetramethyldiaminodiphenylmethane, and N, N ' -tetramethylnaphthylenediamine; and the like aromatic diamines.

The number of carbon atoms of the aromatic amine is preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

The amine compound used in the present embodiment may be an amine compound substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxy group, a hydroxyl group, or a cyano group, or a halogen atom.

Further, a diamine is exemplified as a specific example, but it is needless to say that the amine compound that can be used in the present embodiment is not limited to a diamine, and for example, diethylenetriamine, N ', N ″ -trimethyldiethylenetriamine, N', N ″, may be used in addition to trimethylamine, triethylamine, ethyldimethylamine, aliphatic monoamines corresponding to various diamines such as the above aliphatic diamines, piperidine compounds such as piperidine, methylpiperidine, tetramethylpiperidine, pyridine compounds such as pyridine, picoline, morpholine compounds such as methylmorpholine, thiomorpholine, imidazole compounds such as imidazole, methylimidazole, alicyclic monoamines such as monoamines corresponding to the above alicyclic diamines, heterocyclic monoamines corresponding to the above heterocyclic diamines, monoamines such as aromatic monoamines corresponding to the above aromatic diamines, polyamines having 3 or more amino groups such as N ″ -pentamethyldiethylenetriamine, triethylenetetramine, N '-bis [ (dimethylamino) ethyl ] -N, N' -dimethylethylenediamine, hexamethylenetetramine, tetraethylenepentamine, and the like.

Among the above, from the viewpoint of obtaining higher ionic conductivity, a tertiary amine having a tertiary amino group as an amino group is preferable, a tertiary diamine having two tertiary amino groups is more preferable, a tertiary diamine having two tertiary amino groups at both terminals is further preferable, and an aliphatic tertiary diamine having tertiary amino groups at both terminals is further preferable. Among the above amine compounds, as the aliphatic tertiary diamine having tertiary amino groups at both terminals, tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane and tetraethyldiaminopropane are preferable, and tetramethylethylenediamine and tetramethyldiaminopropane are preferable in view of easy availability and the like.

As the complexing agent other than the amine compound, for example, a compound having a group containing a hetero element such as a halogen element such as an oxygen element or a chlorine element has a high affinity for lithium element, and the complexing agent other than the amine compound is exemplified. Further, a compound having a group other than the amino group containing a nitrogen element as a hetero element, for example, a group such as a nitro group or an amide group can also obtain the same effect.

Examples of the other complexing agent include alcohol solvents such as ethanol and butanol; ester solvents such as ethyl acetate and butyl acetate; aldehyde solvents such as formaldehyde, acetaldehyde, and dimethylformamide; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as diethyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole; aromatic hydrocarbon solvents containing halogen elements such as trifluorotoluene, nitrobenzene, chlorobenzene, chlorotoluene, and bromobenzene; and solvents containing carbon atoms and heteroatoms such as acetonitrile, dimethylsulfoxide, and carbon disulfide. Among these, ether solvents are preferred, diethyl ether, diisopropyl ether, dibutyl ether, and tetrahydrofuran are more preferred, and diethyl ether, diisopropyl ether, and dibutyl ether are still more preferred.

(mixing)

As shown in the flowchart of fig. 1, a complex slurry containing the complex formed by the solid electrolyte raw material and the complexing agent is obtained by mixing the solid electrolyte raw material and the complexing agent in the reaction tank. Since the solid electrolyte raw material contains a solid and the complexing agent is in a liquid state, the form in which the solid electrolyte raw material and the complexing agent are mixed in the present embodiment is usually a slurry form of the solid electrolyte raw material in which a solid is present in a liquid complexing agent.

The amount of the solid electrolyte raw material is preferably 5g or more, more preferably 10g or more, further preferably 30g or more, further preferably 45g or more, and the upper limit is preferably 500g or less, more preferably 400g or less, further preferably 300g or less, and further preferably 250g or less, based on 1L of the amount of the complexing agent and 1L of the total amount of the complexing agent and the solvent in the case of using a solvent described later. When the content of the solid electrolyte raw material is within the above range, the solid electrolyte raw material is easily mixed, the dispersion state of the solid electrolyte raw material is improved, and the reaction between the raw materials is promoted, so that the complex is easily and efficiently obtained, and the solid electrolyte is easily obtained.

The method for mixing the solid electrolyte raw material and the complexing agent is not particularly limited as long as at least one raw material (compound) and the complexing agent contained in the solid electrolyte raw material are put into a device capable of mixing the solid electrolyte raw material and the complexing agent in a reaction vessel and mixed. For example, it is preferable that the complexing agent is supplied into the reaction vessel shown in fig. 3, and after the stirring blade is operated, the solid electrolyte raw material is gradually added, because a good mixed state of the raw materials can be obtained, and the dispersibility of the raw materials is improved, and the complex can be easily obtained.

In addition, when a halogen monomer is used as a raw material, the raw material may not be a solid, and specifically, fluorine and chlorine may be in the form of a gas and bromine may be in the form of a liquid at normal temperature and pressure. For example, in the case where the raw material is a liquid, the raw material may be supplied into the reaction vessel together with the complexing agent separately from other solid raw materials, or in the case where the raw material is a gas, the raw material may be supplied by blowing the raw material into a substance obtained by adding the solid electrolyte raw material to the complexing agent.

The method for producing a sulfide solid electrolyte according to the present embodiment is characterized by including mixing a solid electrolyte raw material and a complexing agent in a reaction tank, and can be produced by a method that does not use equipment that is generally called a pulverizer and is used for pulverizing a solid raw material, such as a media pulverizer such as a ball mill or a bead mill, as long as the solid electrolyte raw material and the complexing agent are mixed in the reaction tank, for example, as shown in fig. 3, by using a reaction tank equipped with a stirrer. In the production method of the present embodiment, a complex is formed from the solid electrolyte raw material and the complexing agent simply by mixing the solid electrolyte raw material and the complexing agent in the reaction vessel, and the complex is dried, heated, or the like as necessary to obtain a sulfide solid electrolyte.

An example of the apparatus for mixing the solid electrolyte raw material and the complexing agent is a mechanical stirring mixer having a stirring blade in a reaction vessel. The mechanical agitation type mixer may be exemplified by a high-speed agitation type mixer, a double-arm type mixer, and the like, and is preferably used from the viewpoint of obtaining a higher ionic conductivity by efficiently obtaining a uniform complex by improving the uniformity of the raw materials in the mixture of the solid electrolyte raw material and the complexing agent. Further, as the high-speed stirring type mixer, a vertical axis rotary type mixer, a horizontal axis rotary type mixer, and the like can be exemplified, and any type of mixer can be used.

The shape of the stirring blade used in the mechanical stirring mixer may be, for example, a blade type, an arm type, a belt type, a multistage blade type, a double arm type, a bucket type, a biaxial blade type, a flat blade type, a C-type blade type, etc., and the bucket type, the flat blade type, the C-type blade type, etc. are preferable from the viewpoint of obtaining a higher ionic conductivity by efficiently obtaining a uniform complex by improving the uniformity of the raw material in the mixture of the solid electrolyte raw material and the complexing agent.

The temperature conditions for mixing the solid electrolyte raw material and the complexing agent are not particularly limited, and are, for example, -30 to 100 ℃, preferably-10 to 50 ℃, and more preferably around room temperature (23 ℃) (for example around 5 ℃ C.). The mixing time is about 0.1 to 150 hours, and from the viewpoint of more uniform mixing and obtaining higher ionic conductivity, it is preferably 0.3 to 120 hours, more preferably 0.5 to 100 hours, and still more preferably 0.8 to 80 hours. Therefore, the reaction tank may be provided with a heating mechanism for heating the fluid in the reaction tank as necessary.

By mixing a solid electrolyte raw material and a complexing agent in a reaction vessel, a complex in which lithium, sulfur, phosphorus, and halogen elements contained in the raw material are directly bonded to each other via the complexing agent and/or without the complexing agent can be obtained under the action of the complexing agent. That is, in the manufacturing method of the present embodiment, a complex obtained by mixing a solid electrolyte material and a complexing agent is formed of the complexing agent, lithium element, sulfur element, phosphorus element, and halogen element, and complex slurry containing the complex is obtained by mixing the solid electrolyte material and the complexing agent. In the present embodiment, the obtained complex is not completely dissolved in the complexing agent as a liquid, but a slurry containing the complex as a solid can be obtained. Therefore, the production method of the present embodiment corresponds to a heterogeneous system in the so-called liquid phase method. The slurry may be referred to as a complex slurry containing a complex, but may also contain a solid electrolyte obtained by reacting a solid electrolyte raw material that does not form a complex, a complexing agent, or the like, or a part of the solid electrolyte raw material.

(Complex)

As described above, the complex is formed of the complexing agent, the lithium element, the sulfur element, the phosphorus element, and the halogen element. Further, it is considered that since the complex has a characteristic that a peak different from a peak derived from the raw material is observed in an X-ray diffraction pattern in X-ray diffraction measurement, the complex typically has a complex structure in which lithium element and other elements are directly bonded via a complexing agent and/or without via a complexing agent. Only the solid electrolyte raw materials are mixed, and only the peak derived from the raw materials should be observed. However, since a peak different from a peak derived from the raw material is observed by mixing the solid electrolyte raw material with the complexing agent, these complexes obtained by mixing are substances having a structure significantly different from that of the raw material itself contained in the solid electrolyte raw material. This will be confirmed specifically in the embodiments. Fig. 4 to 6 show measurement examples of X-ray diffraction patterns of each raw material, complex, and sulfide solid electrolyte, such as lithium sulfide. As can be seen from the X-ray diffraction pattern of fig. 6, the complex had a predetermined crystal structure. Note that the diffraction pattern does not include the diffraction pattern of any raw material such as lithium sulfide shown in fig. 5, and it is found that the complex has a crystal structure different from that of the raw material.

Further, the complex is characterized by having a structure different from that of the crystalline sulfide solid electrolyte. This will also be confirmed specifically in the embodiments. Fig. 4 also shows the X-ray diffraction pattern of the crystalline sulfide solid electrolyte, which is different from the diffraction pattern of the complex. Further, the complex has a predetermined crystal structure, and is different from an amorphous solid electrolyte having a wide pattern.

From the above results, it is assumed that the complex is formed by the complexing agent, the lithium element, the sulfur element, the phosphorus element, and the halogen element, and typically, the complex forms a complex structure in which the lithium element and the other element are directly bonded via the complexing agent and/or without the complexing agent.

Here, the formation of a complex by the complexing agent can be confirmed by, for example, gas chromatography analysis. Specifically, the complexing agent contained in the complex can be quantified by dissolving a powder of the complex in methanol and subjecting the obtained methanol solution to gas chromatography.

The content of the complexing agent in the complex varies depending on the molecular weight of the complexing agent, and is usually about 10 mass% to 70 mass%, and preferably 15 mass% to 65 mass%.

In the present embodiment, it is preferable to form a complex containing a halogen element in terms of improving the ion conductivity. By using complexing agents, PS₄A lithium-containing structure such as a structure and a lithium-containing raw material such as lithium halide are bonded (coordinated) via a complexing agent, and a complex in which a halogen element is fixed in a more dispersed manner is easily obtained.

Even when the solid-liquid separation of the complex slurry is performed, it can be confirmed that the halogen element in the complex forms a complex structure by including a predetermined amount of the halogen element in the complex. This is because the halogen element not constituting the complex is more easily eluted than the halogen element constituting the complex and discharged into the liquid for solid-liquid separation. Further, it can also be confirmed that the ratio of the halogen element in the complex or the sulfide solid electrolyte is not significantly reduced compared to the ratio of the halogen element supplied from the raw material by performing composition analysis by ICP analysis (inductively coupled plasma emission spectroscopy) on the complex or the sulfide solid electrolyte.

The amount of the halogen element remaining in the complex is preferably 30% by mass or more, more preferably 35% by mass or more, and further preferably 40% by mass or more with respect to the arrangement composition. The upper limit of the amount of the halogen element remaining in the complex is 100 mass%.

(Cooling)

The method for producing a sulfide solid electrolyte according to the present embodiment includes: the complex slurry is transferred to an intermediate tank equipped with a cooling device and cooled (hereinafter, it may be simply referred to as "cooling" and "cool storage" because it is substantially accompanied by storage during cooling). Without this cold storage, halogen elements, lithium elements, and the like derived from, for example, lithium bromide, lithium iodide, and the like, which are preferably used as solid electrolyte raw materials, contribute to the manifestation of the ionic conductivity and the increased specific components are separated without remaining in the complex, resulting in a decrease in the ionic conductivity of the resulting sulfide solid electrolyte.

As described above, in the production of a sulfide solid electrolyte, it is important to maintain a specific component without separating it from a complex in order to obtain high ion conductivity, and therefore, a complexing agent is used in the production method of the present embodiment. On the other hand, it has also been found that even if a complexing agent is used, if the complex is maintained in a slurry state, a specific component is separated from the complex with time, resulting in a decrease in ion conductivity. The situation where the complex is held in a slurry state may occur in the production of a laboratory-grade solid electrolyte, but in the future, if the complex is produced on a mass production scale, it is expected that the situation where the complex is held in a slurry state will be prolonged due to production adjustment, equipment failure, or the like, and the ion conductivity will be lowered. In the production method of the present embodiment, the complex slurry is cooled and stored, whereby the separation of the specific component from the complex can be suppressed as much as possible, and high ionic conductivity can be obtained.

Thus, the production method of the present embodiment can cope not only with a case where a sulfide solid electrolyte having a higher ionic conductivity is obtained, but also with a case where drying, heating, or the like, which will be described later, cannot be performed for a short time, for example, within 12 hours, within 6 hours, within 1 hour, or the like after the complex slurry is produced in the production process of the sulfide solid electrolyte, that is, a case where the complex is maintained for a long time in the state of the complex slurry, and can be said to be an effective production method.

For preservation by cooling can be madeThe reason why the above-mentioned specific component is retained in the complex to inhibit the separation is considered to be that in the complex, PS is bonded via a hetero element in the complexing agent₄The binding force between the lithium element and the lithium element such as lithium halide in the structure or the like is maintained, and the chemical stability of the aggregate formed via the complexing agent in the complex slurry is maintained. If the polymer is completely dissolved or completely undissolved in a predetermined temperature range, the influence of solubility is not exerted (for example, patent document 2). However, since the complex slurry of the present embodiment coexists in a solid-liquid state, each component of the complex having different solubilities is dissolved or not dissolved and contained in the slurry. Since the solubility varies depending on the temperature, it is generally considered to be desirable to maintain the dissolved state of the complex slurry by keeping the temperature of the complex slurry constant. In addition, no change was observed in visual observation when the complex slurry was held for a long period of time, regardless of the presence or absence of cold storage. Therefore, it is difficult to find a problem related to chemical stability of the complex slurry. However, surprisingly, in the production method of the present embodiment, it has been found that by performing only a simple operation of cooling and storing a complex slurry containing a complex formed from a predetermined element and a complexing agent, excellent effects are obtained that the chemical stability of the aggregate formed via the complexing agent in the complex slurry can be obtained, separation of bromine element and lithium element derived from a specific component, particularly lithium bromide that is easily separated, can be suppressed, and a sulfide solid electrolyte having a higher ionic conductivity can be obtained.

As shown in fig. 3, the cooling storage may be performed after the above-described mixing to obtain the complex slurry, and in the case of drying described later, may be performed before the drying. When the complex described later is pulverized, it is preferably pulverized thereafter. The complex slurry is preferably stored in a cooled state after pulverization and before heating when heating described later is performed, and in a cooled state after pulverization and before drying described later is preferably stored in a cooled state after pulverization and before drying. In addition, when drying and heating are performed as described later, since drying is usually performed first, it is preferable to store the pulverized material in a cooled state before drying. Therefore, in the present embodiment, it is preferable to perform cooling storage after pulverization and before drying or heating the complex slurry. By storing the complex by cooling at such a timing, the specific component can be more efficiently retained in the complex, and the decrease in ion conductivity due to separation can be suppressed, so that a sulfide solid electrolyte having high ion conductivity can be easily obtained.

The flow shown in FIG. 3 shows a scheme in which the complex slurry obtained by mixing in the reaction tank is transferred to an intermediate tank equipped with a cooling device and cooled and stored.

As the intermediate tank for performing the cooling preservation, for example, as shown in fig. 3, a cooling jacket such as a water cooling jacket may be used as the intermediate tank of the cooling device provided on the outer wall of the intermediate tank, and the medium of the cooling jacket may be appropriately determined depending on the desired cooling temperature.

For more uniform cooling, as shown in fig. 3, a mixer (stirrer) may be provided in the intermediate tank, and the mixer may be appropriately selected from, for example, mixers that can be provided in the reaction tank and used.

As shown in fig. 3, the intermediate tank may be provided as a tank different from the reaction tank in which the mixing is performed, and the intermediate tank may be replaced by a tank having a cooling device in the reaction tank in which the mixing is performed, from the viewpoint of simplifying the apparatus and from the viewpoint of omitting the trouble of transferring the complex slurry.

In the present embodiment, the temperature condition for cold storage is preferably less than room temperature (23 ℃), more preferably 20 ℃ or less, further preferably 15 ℃ or less, and still more preferably 10 ℃ or less, and the lower limit is not particularly limited, but is preferably-15 ℃ or more, more preferably-10 ℃ or more, further preferably-5 ℃ or more, and still more preferably 0 ℃ or more. When the temperature conditions are set as described above, the specific component is more efficiently retained in the complex, the decrease in ion conductivity due to the separation is suppressed, and the sulfide solid electrolyte having high ion conductivity is easily obtained.

The cooling storage time is determined depending on the time for which the sulfide solid electrolyte is kept in the state of a complex slurry in the production process of the sulfide solid electrolyte, but is preferably 0.1 hour or more, more preferably 1 hour or more, and even more preferably 12 hours or more, from the viewpoint of suppressing the separation of the specific component as much as possible. The upper limit of the cooling storage time is also determined by the time of holding in the state of the complex slurry, and is not particularly limited, but for example, 240 hours or less provides an extremely excellent inhibitory effect on the separation of the specific component, and from the viewpoint of improving the inhibitory effect, 72 hours or less, more preferably 60 hours or less, still more preferably 48 hours or less, and still more preferably 36 hours or less.

(crushing)

The method for producing a sulfide solid electrolyte according to the present embodiment preferably further comprises pulverizing the complex. By pulverizing the complex, a sulfide solid electrolyte having a small particle size while suppressing a decrease in ionic conductivity can be obtained.

Unlike mechanical polishing by the so-called solid phase method, the complex in the present embodiment is pulverized to obtain an amorphous or crystalline sulfide solid electrolyte without mechanical stress. As mentioned above, the complex comprises a complexing agent, PS₄The structure containing lithium such as a structure is bonded (coordinated) to a raw material containing lithium such as lithium halide via a complexing agent. Further, it is considered that when the complex is pulverized, fine particles of the complex can be obtained while maintaining the above bonding (coordination) and dispersion state. When this complex is subjected to heat treatment, components bonded (coordinated) via the complexing agent are bonded together while the complexing agent is removed, and a reaction to the crystalline sulfide solid electrolyte is likely to occur. Therefore, it is difficult to cause large grain growth due to aggregation of particles observed in synthesis of a general solid electrolyte, and thus fine particles can be easily formed.

In addition, from the viewpoint of the performance and production of all-solid batteries, it is desirable that the particle size of the sulfide solid electrolyte is small, but it is not easy to micronize the sulfide solid electrolyte by pulverization using a bead mill or the like. For example, wet pulverization using a solvent can achieve some degree of micronization, but sulfide solid electrolytes are easily degraded by the solvent and aggregation during pulverization easily occurs, which causes a problem that an excessive load is applied to pulverization. On the other hand, it is difficult to finely pulverize to submicron level even by dry pulverization without using a solvent. In such a situation, by performing easy processing such as crushing of the complex, the performance of the all-solid battery can be improved, and the manufacturing efficiency can be improved, thereby providing great advantages.

Furthermore, the PS can be easily mixed by stirring with pulverization₄The lithium-containing structure such as the structure or the aggregate via the complexing agent, and the lithium-containing raw material such as lithium halide or the aggregate via the complexing agent are present throughout, and a complex in which the halogen element is fixed in a more dispersed state is obtained.

The pulverizer used for pulverizing the complex is not particularly limited as long as it can pulverize the particles, and for example, a media pulverizer using a pulverizing medium can be used. In the medium type pulverizer, a wet type pulverizer capable of coping with wet type pulverization is preferable in consideration of a slurry state of a complex mainly accompanying a liquid such as a complexing agent or a solvent.

The wet type pulverizer may be representatively exemplified by a wet type bead mill, a wet type ball mill, a wet type vibration mill, etc., and a wet type bead mill using beads as a pulverizing medium is preferable in that conditions for pulverizing operation can be freely adjusted and a material having a smaller particle diameter can be easily handled. In addition, a dry pulverizer such as a dry media pulverizer such as a dry bead mill, a dry ball mill, or a dry vibration mill, or a dry non-media pulverizer such as a jet mill, may be used.

The complex pulverized by the pulverizer is usually supplied as a mixture obtained by mixing a solid electrolyte raw material and a complexing agent, and is mainly supplied in a slurry state, that is, the object pulverized by the pulverizer mainly becomes a complex slurry containing the complex. Therefore, the pulverizer used in the present embodiment is preferably a flow-through pulverizer, and can perform a circulation operation of circulating the complex slurry as necessary. More specifically, a pulverizer in a form circulating between a pulverizer (pulverizing mixer) for pulverizing the slurry and a temperature-maintaining tank (reaction tank) as described in Japanese patent application laid-open No. 2010-140893 is preferably used.

The size of the beads used in the above-mentioned pulverizer may be appropriately selected depending on the desired particle diameter, treatment amount, and the like, and for example, the diameter of the beads may be about 0.05 mm.phi or more and 5.0 mm.phi or less, preferably 0.1 mm.phi or more and 3.0 mm.phi or less, and more preferably 0.3mm phi or more and 1.5mm phi or less.

As a pulverizer for pulverizing the complex, a machine capable of pulverizing an object with ultrasonic waves, for example, a machine called an ultrasonic pulverizer, an ultrasonic homogenizer, a probe ultrasonic pulverizer, or the like can be used.

In this case, the conditions such as the frequency of the ultrasonic wave may be appropriately selected depending on the average particle size of the desired complex, and the frequency may be, for example, about 1kHz to 100kHz, and is preferably 3kHz to 50kHz, more preferably 5kHz to 40kHz, and even more preferably 10kHz to 30kHz, from the viewpoint of more efficiently pulverizing the complex.

The output of the ultrasonic crusher may be generally about 500 to 16,000W, preferably 600 to 10,000W, more preferably 750 to 5,000W, and still more preferably 900 to 1,500W.

Average particle diameter (D) of the Complex obtained by grinding₅₀) The thickness is suitably determined as desired, and is usually 0.01 to 50 μm, preferably 0.03 to 5 μm, and more preferably 0.05 to 3 μm. By setting the average particle size as described above, it becomes possible to meet the demand for a small particle size, for example, an average particle size of 1 μm or less.

The time for pulverization is usually 0.1 hour to 100 hours, and from the viewpoint of efficiently making the particle diameter a desired size, it is preferably 0.3 hour to 72 hours, more preferably 0.5 hour to 48 hours, and still more preferably 0.8 hour to 24 hours.

The complex can be pulverized at any time as long as it can be pulverized, and from the viewpoint of more efficiently making the particle diameter a desired size, and from the viewpoint of more efficiently retaining the specific component in the complex, suppressing a decrease in ionic conductivity due to separation, and easily obtaining a sulfide solid electrolyte having a high ionic conductivity, it is preferable to perform pulverization before cooling storage, for example, at the time of (simultaneously with) the mixing, after the mixing, and more preferably after the mixing.

In the case of drying described later, the powder may be pulverized after drying. In this case, among the above-mentioned pulverizers that can be used in the present production method, any of dry pulverizers is preferably used. Other grinding conditions and other matters related to grinding are the same as those of grinding of the complex slurry, and the average particle size of the complex obtained by grinding is also the same as described above.

(drying)

The method for producing a sulfide solid electrolyte according to the present embodiment includes a step of subjecting a slurry to at least one treatment selected from drying and heating, that is, a step of performing drying, heating, or a treatment of drying and heating. In the production method of the present embodiment, the slurry is preferably a complex slurry. Therefore, the production method of the present embodiment preferably includes a step of subjecting the complex slurry to at least one treatment selected from drying and heating.

When the slurry is a complex slurry, a powder of the complex can be obtained by a constitution including the above-mentioned one treatment. For example, when a crystalline sulfide solid electrolyte is obtained, heating described later is preferably performed, but drying in advance enables efficient heating. In addition, drying and subsequent heating may be performed in the same step.

Examples of the apparatus for drying include, but are not limited to, a hot plate, a vacuum heating and drying apparatus, an argon atmosphere furnace, and a firing furnace, and industrial horizontal dryers including a heating unit and a feeding mechanism, horizontal vibration and flow dryers, and the like.

The drying of the complex slurry can be performed at a temperature corresponding to the kind of the remaining complexing agent (complexing agent not introduced into the complex). For example, the reaction can be carried out at a temperature equal to or higher than the boiling point of the complexing agent. The drying can be performed by drying under reduced pressure (vacuum drying) using a vacuum pump or the like at a temperature of usually 5 to 100 ℃, preferably 10 to 85 ℃, more preferably 15 to 70 ℃, and still more preferably at room temperature (about 23 ℃) (for example, about ± 5 ℃ at room temperature) to volatilize the complexing agent.

Further, the complex slurry may be dried by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifugal separator or the like. In the present embodiment, after the solid-liquid separation, drying may be performed under the above-described temperature conditions.

Specifically, in the solid-liquid separation, it is easy to transfer the complex slurry to a container, precipitate the complex slurry, and then remove the complexing agent or solvent which becomes a supernatant, or to perform filtration using, for example, a glass filter having a pore size of about 10 to 200 μm, preferably 20 to 150 μm.

(heating)

The method for producing a sulfide solid electrolyte according to the present embodiment may include heating the complex. The complex slurry may be heated, and in the case of the drying, the complex powder may be heated. The complex may be a complex obtained by pulverizing the above-mentioned raw materials.

By heating the complex, the complexing agent in the complex is removed, and an amorphous sulfide solid electrolyte containing lithium, sulfur, phosphorus, and a halogen element, or a crystalline sulfide solid electrolyte can be obtained.

Here, it is also possible to confirm that the sulfide solid electrolyte obtained by removing the complexing agent by heating the complex is the same as the X-ray diffraction pattern of the solid electrolyte obtained by the conventional method without using the complexing agent, except that the complexing agent forms a complex as is known from the results of the X-ray diffraction pattern, the gas chromatography analysis, and the like, in terms of the removal of the complexing agent in the complex.

In the production method of the present embodiment, the sulfide solid electrolyte is obtained by heating the complex to remove the complexing agent in the complex, but the less the complexing agent in the sulfide solid electrolyte is, the more preferable the complexing agent is, but the complexing agent may be contained to such an extent that the performance of the solid electrolyte is not impaired. The content of the complexing agent in the sulfide solid electrolyte may be usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less.

In the production method of the present embodiment, in order to obtain the crystalline sulfide solid electrolyte, the complex may be heated to directly obtain the crystalline sulfide solid electrolyte, or the complex may be heated to obtain the amorphous sulfide solid electrolyte, and then the amorphous sulfide solid electrolyte may be heated to obtain the crystalline sulfide solid electrolyte. That is, according to the production method of the present embodiment, an amorphous sulfide solid electrolyte can be produced.

Conventionally, in order to obtain a crystalline solid electrolyte having high ionic conductivity, for example, a solid electrolyte having a II-type crystal structure of a lithium sulfide crystal super ion conductor region described later, it is necessary to prepare an amorphous solid electrolyte by mechanical pulverization treatment such as mechanical grinding or other melt quenching treatment, and then heat the amorphous solid electrolyte. However, the production method of the present embodiment is advantageous as compared with a conventional production method by mechanical polishing or the like in that a crystalline solid electrolyte having a type II crystal structure of a sulfide crystalline lithium super ion conductor region can be obtained without performing mechanical pulverization treatment, other melt quenching treatment, or the like.

In the production method of the present embodiment, the amorphous sulfide solid electrolyte, the crystalline sulfide solid electrolyte obtained after the amorphous sulfide solid electrolyte is obtained, or the crystalline sulfide solid electrolyte obtained directly from the complex can be appropriately selected and obtained as desired, and the heating temperature, the heating time, and the like can be adjusted.

The heating temperature of the complex may be determined, for example, in the case of obtaining an amorphous sulfide solid electrolyte, according to the structure of a crystalline sulfide solid electrolyte obtained by heating the amorphous sulfide solid electrolyte (or the complex), specifically, a Differential Thermal Analysis (DTA) may be performed on the amorphous sulfide solid electrolyte (or the complex) using a differential thermal analysis apparatus (DTA apparatus) under a temperature rise condition of 10 ℃/minute, and the temperature of the peak top of the exothermic peak observed on the lowest temperature side may be set to a range of preferably 5 ℃ or less, more preferably 10 ℃ or less, further preferably 20 ℃ or less, and the lower limit is not particularly limited, and may be set to a temperature of-40 ℃ or more of the peak top of the exothermic peak observed on the lowest temperature side. By setting the temperature range as described above, the amorphous sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining the amorphous sulfide solid electrolyte cannot be generally specified because it varies depending on the structure of the obtained crystalline sulfide solid electrolyte, but is usually preferably 135 ℃ or lower, more preferably 130 ℃ or lower, further preferably 125 ℃ or lower, and the lower limit is not particularly limited, preferably 90 ℃ or higher, more preferably 100 ℃ or higher, further preferably 110 ℃ or higher.

In addition, in the case where the amorphous sulfide solid electrolyte is heated to obtain the crystalline sulfide solid electrolyte or the crystalline sulfide solid electrolyte is directly obtained from the complex, the heating temperature may be determined depending on the structure of the crystalline sulfide solid electrolyte, and is preferably higher than the above-mentioned heating temperature for obtaining the amorphous sulfide solid electrolyte, and specifically, the amorphous sulfide solid electrolyte (or complex) is subjected to Differential Thermal Analysis (DTA) using a differential thermal analysis apparatus (DTA apparatus) under a temperature rise condition of 10 ℃/min, the temperature at the peak top of the heat generation peak observed on the lowest temperature side (this temperature may be referred to as "crystallization temperature") may be in the range of preferably 5 ℃ or more, more preferably 10 ℃ or more, and still more preferably 20 ℃ or more, and the upper limit is not particularly limited, and may be about 40 ℃ or less. By setting the temperature range as described above, the crystalline sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining the crystalline sulfide solid electrolyte is not generally specified because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained, but is usually preferably 130 ℃ or higher, more preferably 135 ℃ or higher, and still more preferably 140 ℃ or higher, and the upper limit is not particularly limited, and is preferably 300 ℃ or lower, more preferably 280 ℃ or lower, and still more preferably 250 ℃ or lower.

The heating time is not particularly limited as long as the desired amorphous sulfide solid electrolyte or crystalline sulfide solid electrolyte can be obtained, and is, for example, preferably 1 minute or more, more preferably 10 minutes or more, still more preferably 30 minutes or more, and still more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, further preferably 5 hours or less, and further preferably 3 hours or less.

Further, the heating is preferably performed under an inert gas atmosphere (for example, a nitrogen atmosphere, an argon atmosphere) or under a reduced-pressure atmosphere (in particular, in a vacuum). This is because deterioration (e.g., oxidation) of the crystalline sulfide solid electrolyte can be prevented. The heating method is not particularly limited, and examples thereof include a method using a hot plate, a vacuum heating apparatus, an argon atmosphere furnace, and a firing furnace. Further, a horizontal dryer having a heating unit and a feeding mechanism, a horizontal vibration flow dryer, or the like can be used industrially, and the amount may be selected according to the amount of heat to be processed.

(amorphous sulfide solid electrolyte)

The amorphous sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte according to the present embodiment contains lithium, sulfur, phosphorus, and a halogen element, and is preferably used as a representative solid electrolyteExemplified by Li₂S-P₂S₅-LiI、Li₂S-P₂S₅-LiCl、Li₂S-P₂S₅-LiBr、Li₂S-P₂S₅Solid electrolytes composed of lithium sulfide, phosphorus sulfide and lithium halide such as LiI-LiBr; solid electrolytes also containing other elements such as oxygen and silicon, e.g. Li₂S-P₂S₅-Li₂O-LiI、Li₂S-SiS₂-P₂S₅LiI, etc. From the viewpoint of obtaining higher ionic conductivity, Li is preferable₂S-P₂S₅-LiI、Li₂S-P₂S₅-LiCl、Li₂S-P₂S₅-LiBr、Li₂S-P₂S₅And a solid electrolyte composed of lithium sulfide, phosphorus sulfide and lithium halide such as-LiI-LiBr.

The kind of the element constituting the amorphous sulfide solid electrolyte can be confirmed by an ICP emission spectrometer, for example.

The amorphous sulfide solid electrolyte obtained by the production method of the present embodiment contains at least Li₂S-P₂S₅In the case of the amorphous sulfide solid electrolyte of (3), Li is used from the viewpoint of obtaining higher ionic conductivity₂S and P₂S₅The molar ratio of (A) to (B) is preferably 65-85: 15-35, more preferably 70-80: 20 to 30, and more preferably 72 to 78: 22-28.

The amorphous sulfide solid electrolyte obtained by the production method of the present embodiment is, for example, Li₂S-P₂S₅In the case of LiI-LiBr, the total content of lithium sulfide and phosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol%, and still more preferably 70 to 85 mol%. The ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, further preferably 40 to 80 mol%, and particularly preferably 45 to 65 mol%.

In the amorphous sulfide solid electrolyte obtained by the production method of the present embodiment, the blending ratio (molar ratio) of the lithium element, the sulfur element, the phosphorus element, and the halogen element is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1-0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2-1.8: 0.2-0.6: 0.05 to 0.5, and more preferably 1.2 to 1.6: 1.3-1.7: 0.25-0.5: 0.08 to 0.4. In addition, when bromine and iodine are used in combination as halogen elements, the blending ratio (molar ratio) of lithium element, sulfur element, phosphorus element, bromine and iodine is preferably 1.0 to 1.8: 1.0-2.0: 0.1-0.8: 0.01-0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2-1.8: 0.2-0.6: 0.02-0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3-1.7: 0.25-0.5: 0.03 to 0.2: 0.03 to 0.2, and more preferably 1.35 to 1.45: 1.4-1.7: 0.3-0.45: 0.04-0.18: 0.04 to 0.18. When the blending ratio (molar ratio) of the lithium element, the sulfur element, the phosphorus element, and the halogen element is set to the above range, a sulfide solid electrolyte having a higher ionic conductivity and having a crystal structure of a sulfide crystal lithium super ion conductor region II type described later can be easily obtained.

The shape of the amorphous sulfide solid electrolyte is not particularly limited, and examples thereof include a particle shape. Average particle diameter (D) of particulate amorphous sulfide solid electrolyte₅₀) For example, the particle diameter can be in the range of 0.01 to 500 μm, 0.1 to 200 μm.

(crystalline solid electrolyte)

The crystalline sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte according to the present embodiment may be a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte to a crystallization temperature or higher, and the crystal structure thereof may be Li₃PS₄Crystal structure, Li₄P₂S₆Crystal structure, Li₇PS₆Crystal structure, Li₇P₃S₁₁A crystal structure, a crystal structure having peaks in the vicinity of 20.2 ° and in the vicinity of 23.6 ° (e.g., japanese patent laid-open publication No. 2013-16423), and the like.

Further, Li is also exemplified_4-xGe_1-xP_xS₄Type II (thio-silicon Region II) crystal structure of lithium-like sulfide crystal super ion conductor RegionAccording to Kanno et al, Journal of The Electrochemical Society (Journal of The electro-chemical Society), 148(7) A742-746(2001), and Li_4-xGe_1-xP_xS₄A similar crystal structure of a lithium-sulfide-like crystal super-ion conductor Region II (thio-silicon Region II) (refer to Solid State Ionics (Solid ions), 177(2006), 2721-2725), and the like.

The crystal structure of the crystalline sulfide solid electrolyte obtained by the production method of the present embodiment is preferably a sulfide crystalline lithium super ion conductor region II type crystal structure among the above from the viewpoint of obtaining higher ion conductivity. Here, the phrase "II-type crystal structure of lithium sulfide crystal super ion conductor region" means Li_4-xGe_1-xP_xS₄Lithium-sulfide-like crystalline super-ion conductor Region II (thio-silicon Region II) type crystal structure, and Li_4-xGe_1-xP_xS₄Any one of crystal structures similar to the type of thio-silicon Region II (lithium-sulfide Region II) of the lithium-like crystalline super-ion conductor. The crystalline sulfide solid electrolyte obtained by the production method of the present embodiment may have the crystalline sulfide solid electrolyte having the above-described type II crystal structure of the sulfide crystalline lithium super ion conductor region, or may have the type II crystal structure of the sulfide crystalline lithium super ion conductor region as a main crystal, and from the viewpoint of obtaining higher ion conductivity, it is preferable to have the type II crystal structure of the sulfide crystalline lithium super ion conductor region as a main crystal. In the present specification, "having" as a main crystal means that the proportion of the subject crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more. In addition, from the viewpoint of obtaining higher ion conductivity, the crystalline sulfide solid electrolyte obtained by the production method of the present embodiment is preferably one that does not contain crystalline Li₃PS₄(β-Li₃PS₄) The crystalline sulfide solid electrolyte of (1).

In X-ray diffraction measurement using CuK alpha rays, Li₃PS₄Diffraction peaks of the crystal structure appear, for example, in the vicinity of 2 θ of 17.5 °, 18.3 °, 26.1 °, 27.3 °, and 30.0 °, and Li₄P₂S₆Diffraction peaks of a crystal structure appear in the vicinity of, for example, 16.9 °, 27.1 ° and 32.5 ° 2 θ, and Li₇PS₆Diffraction peaks of the crystal structure appear, for example, in the vicinity of 15.3 °, 25.2 °, 29.6 °, and 31.0 ° when 2 θ is equal to Li₇P₃S₁₁Diffraction peaks of the crystal structure appear, for example, in the vicinity of 2 θ ═ 17.8 °, 18.5 °, 19.7 °, 21.8 °, 23.7 °, 25.9 °, 29.6 °, and 30.0 °, Li_4-xGe_1-xP_xS₄Diffraction peaks of a lithium-sulfide-like crystalline super-ion conductor Region II (thio-silicon Region II) type crystal structure occur, for example, in the vicinity of 2 θ ═ 20.1 °, 23.9 °, and 29.5 °, and with Li_4-xGe_1-xP_xS₄Diffraction peaks of a similar crystal structure of type II (thio-silicon Region II) of the lithium-like sulfide crystalline super ion conductor Region occur, for example, in the vicinity of 20.2 and 23.6 ° 2 θ.

As described above, when the crystal structure of the sulfide crystalline lithium super ion conductor region type II is obtained in the present embodiment, it is preferable that crystalline Li is not contained₃PS₄(β-Li₃PS₄). Fig. 4 shows an example of X-ray diffraction measurement of the crystalline sulfide solid electrolyte obtained by the production method of the present embodiment. Further, fig. 5 shows crystalline Li₃PS₄(β-Li₃PS₄) Example of X-ray diffraction measurement of (2). The following can be grasped from fig. 4 and 5: the sulfide solid electrolyte obtained by the production method of the present embodiment does not have Li capable of being in a crystalline state₃PS₄The observed diffraction peak at 2 θ of 17.5 ° or 26.1 °, or even if present, the peak is detected to a very small extent compared with the diffraction peak of the type II crystal structure of the lithium sulfide crystalline super ion conductor region.

Above having Li₇PS₆A part of P is substituted by Si, and Li is represented by the composition formula_7-xP_1-ySi_yS₆And Li_7+xP_1-ySi_yS₆(X is-0.6 to 0.6, y is 0.1 to 0.6) is a cubic crystal or an orthorhombic crystal, preferably a cubic crystal, and has a crystal structure of mainly 15.5 or 2 [ theta ] in X-ray diffraction measurement using CuKa raysPeaks appearing at positions of 18.0 °, 25.0 °, 30.0 °, 31.4 °, 45.3 °, 47.0 °, and 52.0 °. Li in the above composition formula_7-x-2yPS_6-x-yCl_xThe crystal structure represented by (0.8. ltoreq. x.ltoreq.1.7, 0. ltoreq. y.ltoreq.0.25X +0.5) is preferably a cubic crystal having mainly peaks appearing at positions of 2 θ 15.5 °, 18.0 °, 25.0 °, 30.0 °, 31.4 °, 45.3 °, 47.0 ° and 52.0 ° in X-ray diffraction measurement using CuK α rays. Furthermore, Li in the above compositional formula_7-xPS_6-xHa_xThe crystal structure represented by (Ha is Cl or Br, and X is preferably 0.2 to 1.8) is preferably a cubic crystal, and mainly has peaks appearing at positions of 2 θ ═ 15.5 °, 18.0 °, 25.0 °, 30.0 °, 31.4 °, 45.3 °, 47.0 °, and 52.0 ° in X-ray diffraction measurement using CuK α rays.

In addition, the peak position of each crystal structure above may be shifted within a range of ± 1.0 °.

The shape of the crystalline sulfide solid electrolyte is not particularly limited, and examples thereof include a particle shape. Average particle diameter (D) of particulate crystalline sulfide solid electrolyte₅₀) For example, the particle diameter can be in the range of 0.01 to 500 μm, 0.1 to 200 μm.

(embodiment B)

Next, embodiment B will be explained.

Embodiment B is the following scheme: in the production method of the present embodiment characterized by including mixing a solid electrolyte raw material containing a lithium element, a sulfur element, a phosphorus element, and a halogen element with a complexing agent, Li containing Li as a solid electrolyte raw material is used₃PS₄Etc., preferably amorphous Li₃PS₄Crystalline Li₃PS₄Etc. and a complexing agent. In embodiment a, Li existing as a main structure in the sulfide solid electrolyte obtained by the production method of the present embodiment is synthesized by a reaction between raw materials such as lithium sulfide₃PS₄And the structure containing lithium forms a complex at the same time, it is considered that the structural ratio of the structure is likely to be small.

Therefore, in embodiment B, a solid electrolyte or the like including the structure is first prepared and used as a solid electrolyte raw material. Thus, the above-described structure used as a raw material of a solid electrolyte is bonded (coordinated) to a raw material containing lithium such as lithium halide via a complexing agent, and a complex in which a halogen element is fixed in a dispersed state is more easily obtained. As a result, a sulfide solid electrolyte having high ionic conductivity can be obtained. In addition, as a secondary effect, the generation of hydrogen sulfide can also be suppressed.

The solid electrolyte material containing lithium element, sulfur element, and phosphorus element that can be used in embodiment B may be PS-containing material from the viewpoint of obtaining higher ion conductivity₄The molecular structure of the amorphous solid electrolyte or the crystalline solid electrolyte may be preferably amorphous Li₃PS₄Crystalline Li₃PS₄. In view of suppressing the generation of hydrogen sulfide, it is preferable that P is not contained₂S₇An amorphous solid electrolyte or a crystalline solid electrolyte of structure. As the solid electrolyte, for example, a solid electrolyte produced by a conventional production method such as a mechanical polishing method, a slurry method, a melt quenching method, or the like can be used, and a commercially available product can also be used.

In this case, the solid electrolyte containing lithium element, sulfur element, and phosphorus element is preferably an amorphous solid electrolyte. The dispersibility of the halogen element in the complex is improved, and the halogen element is likely to bond with the lithium element, the sulfur element, and the phosphorus element in the solid electrolyte, and as a result, a sulfide solid electrolyte having a higher ionic conductivity can be obtained.

In embodiment B, there is PS₄The content of the amorphous solid electrolyte or the like having a structure is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and further preferably 70 to 80 mol% with respect to the total amount of the solid electrolyte raw materials.

In use with PS₄In the case of an amorphous solid electrolyte having a structure and a halogen monomer, the halogen monomer is a halogen monomer having PS₄Content of structural amorphous solid electrolyte and the likePreferably 1 to 50 mol%, more preferably 2 to 40 mol%, further preferably 3 to 25 mol%, and further preferably 3 to 15 mol%.

The case of using a halogen monomer and a lithium halide or the case of using two halogen monomers is the same as in embodiment a.

In embodiment B, other than the above-described raw materials, for example, a complexing agent, mixing, cold storage, drying, heating, an amorphous solid electrolyte, a crystalline solid electrolyte, and the like are the same as those described in embodiment a.

In embodiment B, the conditions for preferably pulverizing the complex, the pulverizer for pulverization, pulverization after mixing or drying, pulverization, and pulverization are also the same as in embodiment a described above.

(embodiments C and D)

As shown in the flowchart of fig. 2, embodiments C and D differ from embodiments a and B described above in that a solvent is added to the solid electrolyte raw material and the complexing agent. Embodiments C and D are heterogeneous methods in which solid and liquid coexist, and in embodiments a and B, an electrolyte precursor is formed as a solid in a complexing agent as a liquid. In this case, if the complex is easily dissolved in the complexing agent, the components may be separated. In embodiments C and D, elution of components in the complex can be suppressed by using a solvent that does not dissolve the complex.

(solvent)

In the sulfide solid electrolytes of embodiments C and D, a solvent that does not dissolve the complex is added to the solid electrolyte raw material and the complexing agent, and the solid electrolyte raw material, the complexing agent, and the solvent that does not dissolve the complex are mixed. By mixing the solid electrolyte material and the complexing agent using the solvent, the effect of using the complexing agent, that is, the formation of a complex that reacts with lithium element, sulfur element, phosphorus element, and halogen element is promoted, and PS is easily produced₄A structure containing lithium or an aggregate thereof via a complexing agent, a raw material containing lithium such as a lithium halide or a raw material thereof via a complexing agentThe complex in which the halogen element is fixed in a more dispersed state can be obtained by the presence of the aggregate of (a) and (b), and as a result, the effect of obtaining high ionic conductivity can be more easily exhibited.

The production method of the present embodiment is a so-called heterogeneous method, and it is preferable that the complex is not completely dissolved in the complexing agent as a liquid and is precipitated. In embodiments C and D, the solubility of the complex can be adjusted by adding a solvent. In particular, since the halogen element is easily separated from the complex, the separation of the halogen element can be suppressed by adding a solvent, and a desired complex can be obtained. As a result, a crystalline sulfide solid electrolyte having high ionic conductivity can be obtained by the complex in which the halogen and other components are dispersed.

As the solvent having such properties, a solvent having a solubility parameter of 10 or less is preferably exemplified. In the present specification, the solubility parameter is described in various documents, for example, chemical review (heicheng 16 years release, 5 th revision, pill good company) and the like, and is a value δ ((cal/cm) calculated by the following mathematical formula (1)³)^1/2) Also called Hildebrand parameter, SP value.

[ number 1]

(in the numerical formula (1), Δ H represents molar heat generation, R represents a gas constant, T represents a temperature, and V represents a molar volume.)

By using a solvent having a solubility parameter of 10 or less, the solid electrolyte material containing a halogen element such as a halogen element or lithium halide, and a component containing a halogen element constituting a complex (for example, an aggregate in which lithium halide is bonded to a complexing agent) are relatively difficult to dissolve compared with the complexing agent, and the halogen element is easily immobilized in the complex, and the halogen element is present in the obtained complex in a well-dispersed state and further in the sulfide solid electrolyte, and thus a sulfide solid electrolyte having high ionic conductivity is easily obtained. That is, the solvent used in the present embodiment preferably has a property of not dissolving the complex. From the same viewpoint as above, the solubility parameter of the solvent is preferably 9.5 or less, more preferably 9.0 or less, and further preferably 8.5 or less.

As the solvent used in the production method of embodiments C and D, more specifically, a solvent conventionally used in the production of a solid electrolyte can be widely used, and examples thereof include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; a solvent containing a carbon atom such as an alcohol solvent, an ester solvent, an aldehyde solvent, a ketone solvent, an ether solvent, and a solvent containing a carbon atom and a hetero atom; among these, it is preferable to appropriately select and use the solvent having the solubility parameter in the above range.

More specifically, the solvent may, for example, be an aliphatic hydrocarbon solvent such as hexane (7.3), pentane (7.0), 2-ethylhexane, heptane (7.4), octane (7.5), decane, undecane, dodecane or tridecane; alicyclic hydrocarbon solvents such as cyclohexane (8.2) and methylcyclohexane (7.8); aromatic hydrocarbon solvents such as benzene, toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8), tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene (9.5), chlorotoluene (8.8), bromobenzene, and the like; alcohol solvents such as ethanol (12.7) and butanol (11.4); ester solvents such as ethyl acetate (9.1) and butyl acetate (8.5); aldehyde solvents such as formaldehyde, acetaldehyde (10.3), and dimethylformamide (12.1); ketone solvents such as acetone (9.9) and methyl ethyl ketone; ether solvents such as diethyl ether (7.4), diisopropyl ether (6.9), dibutyl ether, tetrahydrofuran (9.1), dimethoxyethane (7.3), cyclopentyl methyl ether (8.4), tert-butyl methyl ether, and anisole; and solvents containing carbon atoms and hetero atoms such as acetonitrile (11.9), dimethyl sulfoxide, and carbon disulfide. In the above examples, the value in parentheses is the SP value.

Among these solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and ether solvents are preferable, and from the viewpoint of more stably obtaining high ionic conductivity, heptane, cyclohexane, methylcyclohexane, toluene, ethylbenzene, diethyl ether, diisopropyl ether, dibutyl ether, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole are more preferable, methylcyclohexane, diethyl ether, diisopropyl ether, and dibutyl ether are further more preferable, methylcyclohexane, diisopropyl ether, and dibutyl ether are further more preferable, and methylcyclohexane is particularly preferable. The solvent used in the present embodiment is preferably the organic solvent exemplified above and is different from the complexing agent. In the present embodiment, these solvents may be used alone or in combination of a plurality of them.

When a solvent is used, the content of the raw material in the raw material-containing material may be 1L based on the total amount of the complexing agent and the solvent.

The complex slurry can be dried in embodiments C and D at a temperature corresponding to the types of the remaining complexing agent (complexing agent not introduced into the complex) and solvent. For example, the drying may be performed at a temperature equal to or higher than the boiling point of the complexing agent or the solvent, and may be performed by drying under reduced pressure (vacuum drying) using a vacuum pump or the like at a temperature of usually 5 to 100 ℃, preferably 10 to 85 ℃, more preferably 15 to 70 ℃, and still more preferably at about room temperature (23 ℃) (for example, about room temperature ± 5 ℃) to volatilize the complexing agent and the solvent. In addition, in the heating in embodiments C and D, when the solvent remains in the electrolyte precursor, the solvent is also removed.

Among them, a solvent is different from a complexing agent that forms a complex, and it is difficult to form a complex. Therefore, the solvent that can remain in the complex is usually 3% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less.

In embodiment C, the complexing agent, mixing, cold storage, drying, heating, amorphous solid electrolyte, crystalline solid electrolyte, and the like are the same as those described in embodiment a, except for the solvent. Embodiment D is also the same as embodiment B, except for the points relating to the solvent.

In embodiments C and D, the conditions for preferably pulverizing the complex, the pulverizer for pulverizing, pulverizing after mixing or drying, and pulverizing are also the same as in embodiment a described above.

The sulfide solid electrolyte obtained by the production method of the present embodiment has high ion conductivity and excellent battery performance, and is therefore preferably used for batteries. It is particularly preferable to use lithium as the conductive seed. The sulfide solid electrolyte obtained by the production method of the present embodiment can be used for a positive electrode layer, a negative electrode layer, and an electrolyte layer. Each layer can be manufactured by a known method.

[ Positive electrode composite Material and negative electrode composite Material ]

For example, when the electrolyte is used for the positive electrode layer and the negative electrode layer, the positive electrode active material and the negative electrode active material are dispersed in the complex slurry, mixed, and dried to attach the complex to the active material surface, and the complex is heated to form the amorphous sulfide solid electrolyte or the crystalline sulfide solid electrolyte, as in the above-described embodiment. In this case, the positive electrode composite material or the negative electrode composite material in which the sulfide solid electrolyte is adhered to the surface of the active material can be obtained by heating the active material together with the active material.

The positive electrode active material is not particularly limited as long as it can promote a battery chemical reaction accompanied by movement of lithium ions due to lithium elements preferably used as an element exhibiting ion conductivity in the present embodiment by the relationship with the negative electrode active material. Examples of the positive electrode active material capable of such intercalation and deintercalation of lithium ions include oxide-based positive electrode active materials and sulfide-based positive electrode active materials.

As the oxide-based positive electrode active material, LMO (lithium manganate), LCO (lithium cobaltate), NMC (lithium nickel cobalt manganate), NCA (lithium nickel cobalt aluminate), LNCO (lithium nickel cobaltate), olivine-type compound (limernpo) may be preferably mentioned₄And Me ═ Fe, Co, Ni, Mn), and the like.

The sulfide-based positive electrode active material may, for example, be titanium sulfide (TiS)₂) Molybdenum sulfide (MoS)₂) Iron sulfide (FeS )₂) Copper sulfide (CuS), nickel sulfide (Ni)₃S₂) And the like.

In addition to the positive electrode active material, niobium selenide (NbSe) can be used₃) And the like.

In the present embodiment, the positive electrode active material may be used alone or in combination of two or more.

The negative electrode active material is not particularly limited as long as it can promote a battery chemical reaction accompanied by movement of lithium ions preferably by lithium element, which is an element preferably used as an element exhibiting ion conductivity in the present embodiment, preferably lithium element such as a metal capable of forming an alloy with lithium element, an oxide thereof, or an alloy of the metal and lithium element. As the negative electrode active material capable of such insertion and extraction of lithium ions, those known as negative electrode active materials in the field of batteries can be used without limitation.

Examples of such a negative electrode active material include metallic lithium, metallic indium, metallic aluminum, metallic silicon, metallic tin, and other metallic lithium, a metal capable of forming an alloy with metallic lithium, an oxide of such a metal, and an alloy of such a metal and metallic lithium.

The electrode active material used in the present embodiment may have a coating layer with which the surface thereof is coated.

As a material for forming the coating layer, there may be mentioned an element which exhibits ion conductivity in the crystalline sulfide solid electrolyte obtained by the production method of the present embodiment, preferably, an ion conductor such as a nitride, an oxide or a composite of the element and the oxide. Specifically, lithium nitride (Li) may be mentioned₃N) with Li₄GeO₄As the main structure, e.g. Li_4-2xZn_xGeO₄Conductor having crystal structure of lithium super ion conductor (LISICON) type, conductor having Li₃PO₄Of skeletal structure type, e.g. Li_4-xGe_1-xP_xS₄Conductor having a sulfide crystal lithium super-ion conductor (thio-silicon) type crystal structure, La, and the like_2/3-xLi_3xTiO₃Etc. have calcium titaniumConductor of mineral crystal structure, LiTi₂(PO₄)₃And conductors having a sodium fast ion conductor (NASICON) type crystal structure.

Further, Li is exemplified_yTi_3-yO₄(0＜y＜3)、Li₄Ti₅O₁₂Lithium titanate such as (LTO) and LiNbO₃、LiTaO₃Lithium metalates of metals belonging to group 5 of the periodic Table, or Li₂O-B₂O₃-P₂O₅Class, Li₂O-B₂O₃-ZnO group, Li₂O-Al₂O₃-SiO₂-P₂O₅-TiO₂And oxide-based conductors such as copper.

The electrode active material having a coating layer is obtained, for example, by: the solution containing the elements constituting the material forming the coating layer is attached to the surface of the electrode active material, and the attached electrode active material is preferably fired at 200 ℃ to 400 ℃.

Here, as the solution containing various elements, for example, a solution containing alkoxides of various metals such as lithium ethoxide, titanium isopropoxide, niobium isopropoxide, tantalum isopropoxide, and the like may be used. In this case, as the solvent, an alcohol solvent such as ethanol or butanol, an aliphatic hydrocarbon solvent such as hexane, heptane or octane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene.

The above-mentioned adhesion may be performed by dipping, spraying, or the like.

The firing temperature is preferably 200 to 400 ℃ as described above, more preferably 250 to 390 ℃ as described above, and the firing time is usually about 1 minute to 10 hours, preferably 10 minutes to 4 hours, from the viewpoint of improving the production efficiency and the battery performance.

The coating rate of the coating layer is preferably 90% or more, more preferably 95% or more, and further preferably 100% based on the surface area of the electrode active material, that is, the entire surface is preferably coated. The thickness of the clad layer is preferably 1nm or more, more preferably 2nm or more, and the upper limit is preferably 30nm or less, more preferably 25nm or less.

The thickness of the clad layer can be measured by cross-sectional observation using a Transmission Electron Microscope (TEM), and the cladding ratio can be calculated from the thickness of the clad layer, the elemental analysis value, and the BET surface area.

In the above battery, it is preferable that a current collector is used in addition to the positive electrode layer, the electrolyte layer, and the negative electrode layer, and a known current collector can be used as the current collector. For example, a layer in which a substance that reacts with the solid electrolyte is coated with Au or the like can be used, such as Au, Pt, Al, Ti, or Cu.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(reference example 1)

In a 1L reaction vessel equipped with a stirring blade, 13.19g of lithium sulfide, 21.26g of phosphorus pentasulfide, 4.15g of lithium bromide and 6.40g of lithium iodide were introduced under a nitrogen atmosphere. 100mL of Tetramethylethylenediamine (TMEDA) as a complexing agent and 800mL of methylcyclohexane as a solvent were added thereto, and the mixture was stirred and mixed by operating a stirring blade. A cyclically operable bead mill ("star mill LMZ015 (model)", manufactured by Ashizawa Finetech corporation) was charged with 456g (bead filling rate: 80% with respect to the pulverization chamber) of zirconia balls (diameter: 0.5 mm. phi.), and the total volume of the mixture was adjusted in accordance with the pump flow rate: 550mL/min, week speed: 8m/s, mill jacket temperature: the slurry was pulverized for 60 minutes while circulating between the reaction tank and the pulverization chamber at 20 ℃.

Then, the resulting complex slurry was immediately dried under vacuum at room temperature (23 ℃) to obtain a complex as a powder. Subsequently, the powder of the complex was heated at 120 ℃ for 2 hours under vacuum to obtain an amorphous solid electrolyte. Further, the amorphous solid electrolyte was heated at 200 ℃ for 2 hours under vacuum to obtain a crystalline solid electrolyte.

The crystalline sulfide solid electrolyte obtained in reference example 1 was subjected to powder X-ray diffraction (XRD) measurement using an X-ray diffraction (XRD) apparatus ("D2 Phaser (trade name)", manufactured by Bruker Japan). The X-ray diffraction spectrum thereof is shown in fig. 4. Further, powder X-ray diffraction (XRD) measurement was also performed on the complex and amorphous sulfide solid electrolyte obtained in reference example 1, and the X-ray diffraction spectrum thereof is shown in fig. 6 together with the X-ray diffraction spectrum of the crystalline sulfide solid electrolyte. As shown in fig. 4 and 6, the crystalline sulfide solid electrolyte obtained in reference example 1 mainly detected crystallization peaks at 2 θ of 20.2 ° and 23.6 ° as in example 1 described later, and had a type II crystal structure of a lithium sulfide crystalline super ion conductor region. Further, the result of measuring the ion conductivity of the obtained crystalline sulfide solid electrolyte was 4.1 (mS/cm).

In the present embodiment, the measurement of the ion conductivity is performed as follows.

The crystalline sulfide solid electrolyte thus obtained was molded into a diameter of 10mm (cross-sectional area S: 0.785 cm)²) And a round particle having a height (L) of 0.1 to 0.3 cm. Electrode terminals were obtained from the upper and lower sides of the sample, and measured by an AC impedance method at 25 ℃ (frequency range: 5 MHz-0.5 Hz, amplitude: 10mV) to obtain Cole-Cole (Cole-Cole) diagram. In the vicinity of the right end of the arc observed in the high-frequency region, the ion conductivity σ (S/cm) was calculated by using the real part Z' (Ω) at the point where-Z "(Ω) was the minimum as the volume resistance R (Ω) of the electrolyte according to the following equation.

R＝ρ(L/S)

σ＝1/ρ

(reference example 2)

In a 1L reaction vessel equipped with a stirring blade, 15.3g of lithium sulfide and 24.7g of phosphorus pentasulfide were added under a nitrogen atmosphere. After the stirring blade was operated, 400mL of tetrahydrofuran previously cooled to-20 ℃ was introduced into the vessel. After naturally raising the temperature to room temperature (23 ℃), the stirring was continued for 72 hours, the obtained reaction mixture slurry was put into a glass filter (pore size: 40 to 100 μm) to obtain a solid content, and the solid content was dried at 90 ℃ to obtain 38g of Li as a white powder₃PS₄(purity: 90 mass%). The powder obtained was subjected to powder X-ray diffraction (XRD) measurement using an X-ray diffraction (XRD) apparatus (SmartLab apparatus, manufactured by Rigaku Co., Ltd.)As a result, a halo pattern was shown, and Li in an amorphous state was confirmed₃PS₄。

(reference example 3)

The white powder Li obtained in reference example 2 was subjected to₃PS₄Vacuum drying at 180 ℃ for 2 hours, thereby obtaining beta-Li₃PS₄(crystalline state).

For the amorphous Li of reference example 2 used as a raw material of a solid electrolyte₃PS₄Lithium sulfide, phosphorus pentasulfide, lithium bromide and lithium iodide, and β -Li of reference example 3₃PS₄(crystalline) powder X-ray diffraction (XRD) measurements were performed. The X-ray diffraction spectrum thereof is shown in fig. 5.

(example 1)

A crystalline sulfide solid electrolyte was obtained in the same manner as in reference example 1, except that in reference example 1, the complex slurry obtained by pulverization was stored in a refrigerator (set temperature: -5 ℃ C.) under cooling for 1 day. The obtained crystalline sulfide solid electrolyte was subjected to powder X-ray diffraction (XRD) measurement in the same manner as in reference example 1. The X-ray diffraction spectrum thereof is shown in fig. 4. Further, the ion conductivity of the obtained crystalline sulfide solid electrolyte was measured. The measurement results are shown in table 1.

(example 2)

A crystalline sulfide solid electrolyte was obtained in the same manner as in reference example 1, except that in reference example 1, the complex slurry obtained by pulverization was stored in a refrigerator (set temperature: -5 ℃ C.) under cooling for 2 days. The ion conductivity of the obtained crystalline sulfide solid electrolyte was measured. The measurement results are shown in table 1.

(example 3)

A crystalline sulfide solid electrolyte was obtained in the same manner as in reference example 1, except that in reference example 1, the slurry of the complex obtained by pulverization was kept for 1 day under cooling while the temperature in the reaction vessel was maintained at 10 ℃. The ion conductivity of the obtained crystalline sulfide solid electrolyte was measured. The measurement results are shown in table 1.

(example 4)

A crystalline sulfide solid electrolyte was obtained in the same manner as in reference example 1, except that in reference example 1, the slurry of the complex obtained by pulverization was kept cooling for 2 days while a refrigerant was circulated through the jacket of the reaction vessel so that the temperature in the reaction vessel was kept at 10 ℃. The ion conductivity of the obtained crystalline sulfide solid electrolyte was measured. The measurement results are shown in table 1.

Comparative example 1

A crystalline sulfide solid electrolyte was obtained in the same manner as in reference example except that in reference example 1, the complex slurry obtained by pulverization was stored at room temperature (23 ℃) for 1 day. The obtained crystalline sulfide solid electrolyte was subjected to powder X-ray diffraction (XRD) measurement in the same manner as in reference example 1. The X-ray diffraction spectrum thereof is shown in fig. 4. Further, the ion conductivity of the obtained crystalline sulfide solid electrolyte was measured. The measurement results are shown in table 1.

Comparative example 2

A crystalline sulfide solid electrolyte was obtained in the same manner as in reference example 1, except that in reference example 1, the complex slurry obtained by pulverization was stored at room temperature (23 ℃) for 2 days. The ion conductivity of the obtained crystalline sulfide solid electrolyte was measured. The measurement results are shown in table 1.

[ Table 1]

Table 1

As shown in table 1, it was confirmed that according to the production method of the present embodiment, even when the complex slurry was kept in a state for a long time, a sulfide solid electrolyte having high ion conductivity was obtained in the same manner as the sulfide solid electrolyte obtained in the reference example in which drying, heating, and the like were performed immediately after the preparation of the complex slurry. On the other hand, it was confirmed that the ionic conductivity was significantly reduced in comparative examples 1 and 2, which were maintained for a long period of time without cooling the complex slurry.

As can be seen from fig. 4, with respect to the X-ray diffraction spectra of the sulfide solid electrolytes obtained in reference example 1, and comparative example 1, the sulfide solid electrolytes of any one of the examples mainly detected crystallization peaks at 2 θ of 20.2 ° and 23.6 °, and had a sulfide crystalline lithium super ion conductor region II type crystal structure.

In addition, in the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in comparative example 1, a crystallization peak derived from lithium bromide was detected at 2 θ ═ 28.1 °. This is considered to be because the lithium bromide was separated from the complex and was not introduced into the sulfide solid electrolyte by maintaining the complex slurry for a long time without cooling and storing, and therefore, although the obtained sulfide solid electrolyte had a sulfide crystalline lithium super ion conductor region type II crystal structure, the ion conductivity was lower than that of reference example 1 and examples.

Industrial applicability

According to the method for producing a sulfide solid electrolyte of the present embodiment, a sulfide solid electrolyte having high ionic conductivity and excellent battery performance can be produced. The sulfide solid electrolyte obtained by the production method of the present embodiment is preferably used for a battery, particularly a battery used for information-related devices such as a personal computer, a video camera, and a mobile phone, or communication devices.

Claims

1. A method for producing a sulfide solid electrolyte, comprising a step of subjecting a slurry to at least one treatment selected from drying and heating, the method comprising:

mixing a solid electrolyte raw material containing lithium element, sulfur element, phosphorus element and halogen element with a complexing agent in a reaction tank to obtain complex slurry containing a complex formed by the solid electrolyte raw material and the complexing agent; transferring the complex slurry to an intermediate tank provided with a cooling device for cooling.

2. The method for producing a sulfide solid electrolyte according to claim 1,

also comprises crushing the complex, wherein the complex slurry comprises the crushed complex.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2,

the cooling is performed after the pulverizing, before drying or heating the complex slurry.

4. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, wherein,

the cooling is performed by maintaining the complex slurry at less than 23 ℃.

5. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 4,

the mixing is to mix the solid electrolyte raw material, the complexing agent, and a solvent that does not dissolve the complex.

6. The method for producing a sulfide solid electrolyte according to claim 5,

the solubility parameter of the solvent is 10 or less.

7. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 6, wherein,

the complexing agent comprises a compound having a tertiary amino group.

8. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 7,

the complexing agent comprises an aliphatic tertiary diamine having two tertiary amino groups.

9. The method for producing a sulfide solid electrolyte according to claim 8,

the aliphatic tertiary diamine is at least one selected from tetramethylethylenediamine and tetramethyldiaminopropane.

10. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 9,

the solid electrolyte raw material contains lithium sulfide and phosphorus pentasulfide.

11. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 10,

the solid electrolyte raw material contains amorphous Li₃PS₄Or crystalline Li₃PS₄。

12. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 11,

the solid electrolyte feedstock comprises lithium bromide.

13. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 12, wherein,

the sulfide solid electrolyte includes a sulfide crystalline lithium super-ion conductor region type II crystal structure.